In a storage system, one or more storage subsystems using HDDs (Hard Disk Drives) and SSDs (Solid State Drives) as storage device, for example, are provided. The storage system including such storage subsystems is accessed from multiple superior devices (such as host computers) via a Storage Area Network (SAN) or a Local Area Network (LAN). Generally, in storage subsystems, the reliability is enhanced by using a method for enhancing reliability accompanying a RAID (Redundant Array of Independent (or Inexpensive) Disks) technique.
Patent Literature 1 discloses enhancing the efficiency of copy control in correspondence to an off-load data transfer function, that is, performing off-load of the function to copy data performed by the host computer to the storage subsystem.
Patent Literature 2 discloses an information system capable of improving availability, wherein a first volume of a first storage and a second volume of a second storage are provided as identical volumes to superior devices. The host computer recognizes the first volume and the second volume as an identical volume having different paths.